1. STRUCTURES IN THE UNIVERSE

1.1 Large-scale structures (1750-1967)

Antiquity and Middle Ages have seen attempts of visualizing worlds
beyond our world. The concept of the plurality of solar systems marks
the beginning of modern times. Yet, the first to actually picture - in
the literal sense - a cosmos of organized stellar systems appears to
be Thomas Wright of Durham. Fig. 1 is taken from
his book ``An Original Theory of the Universe''
(1750).

Figure 1. From the 9th letter of Thomas
Wright's ``An Original Theory of the Universe''
(1750)
Plate XXXI, about which he writes:
``. . . that as the visible Creation is supposed to be full of sidereal
Systems and planetary Worlds, so on, in like similar Manner, the
endless Immensity is an unlimited Plenum of Creations not unlike the
known Universe. See Plate XXXI. which you may if you please, call a
partial View of Immensity, or without much Impropriety perhaps, a
finite View of Infinity ...
That this in all probability may be the real Case, is in some Degree
made evident by the many cloudy Spots, just perceivable by us, as far
without our starry Regions, in which tho' visibly luminous Spaces no
one Star or particular constituent Body can possibly be distinguished;
those in all likelyhood may be external Creation, bordering upon the
known one, too remote for even our Telescopes to reach.''

During the same century first attempts were made to catalogue nebulous
objects, especially those which are not resolved into stars (the five
original ******************** - nebulous stars - of Ptolemaios were
clusters or loose groups of stars). Within little more than a century
the ``Catalogue of Nebulae and Clusters''
(J. Herschel 1864)
had been
assembled: the work of a single family - William, Caroline and John
Herschel. The first complete picture of the distribution of nebulae,
which are not obviously associated with the Milky Way, based on the
New General Catalogue and the two Index Catalogues
(Dreyer 1888,
1895,
1908),
was published by
Charlier (1922).
Fig. 2 shows his
presentation of 11 475 nebulae. The inhomogeneity in the distribution,
by then long recognized
(W. Herschel 1811),
is clearly apparent. Among
the counts of nebulae made in the early 20th century Fath's list
(1914)
obtained from photographs of 139 selected areas is mentioned
here, because of the extensive interpretation of the data by
Seares (1925)
and his comment(1):

``Further, the Selected Areas are too widely spaced for a satisfactory
determination of the effect of local irregularities in distribution;
but, in spite of the limitations, the data merit special attention
because of the freedom from any selection favoring regions in which
nebulae were known to exist.''

Both considerations are important because they are still disputed in
connection with modern surveys. More detail on the early history of
mapping nebulae is given e.g. by
Lundmark (1927) and
Flin (1988).

By the mid-twenties about 10,000 mostly faint galaxies had been
accumulated in the Heidelberg nebular lists (No. 1-15,
Wolf 1901,
1914,
1916;
continued by
Reinmuth, 1916,
1940).

A sample of 44,000 galaxies was available by the
mid-thirties. Excesses and deficiencies of galaxies in certain areas
were discussed
(Hubble 1934);
Fig. 3 is taken from his paper.

The largest total sample - before the advent of the Lick Survey - was
accumulated at the Harvard College Observatory under the leadership of
Harlow Shapley. A plot of 78,000 from a total of 392,780 is shown in
Fig. 4. Based on this material
Shapley (1938)
first claimed that
structures on such large scales suggest ``gradients'' rather than
clustering.

Figure 2. Charlier's map of the nebulae
(Charlier 1922).
``A glance at this plate suffices for stating how the Milky Way, which
is designed by the great axis of the chart is systematically avoided
by the nebulae. A remarkable property of the image is that the
nebulae seem to be piled up in clouds (as also the stars in the Milky
Way). Such a clouding of the nebulae may be a real phenomenon, but it
may also be an accidental effect. . .''

Figure 4. Part of the Harvard Survey
(Shapley 1957).
``Plot of 78,000 individual galaxies in the Canopy area.''
``. . . the far extension of the `Cepheus flare' or cloud of absorbing
material... comes out of the Milky Way. This flare of absorption
covers the north celestial pole. Supported by this survey is the
evidence that from galactic latitude +40° to the north galactic pole
there is no appreciable net increase of population density with
latitude.''

Figure 6a.
Princeton presentation of Lick Catalogue
(Seldner et
at. 1977).
``Map of galaxy counts in the northern galactic hemisphere. The north
galactic pole is at the center, the galactic equator is at the edge,
and galactic latitude is a linear function of radius. Galactic
longitude increases in the clockwise direction with
lII = 0° at the bottom of the map.''

Figure 6b. Princeton presentation (cont.)
``Map of galaxy counts in the southern galactic hemisphere. Galactic
longitude increases in the counterclockwise direction from
lII = 0° at
the bottom of the map.''

The last one of the catalogues assembled without the use of automatic
procedures is the Lick Survey, described by
Shane and Wirtanen
in 1950
and completed 17 years later
(Shane and
Wirtanen 1967).
Even the first results
presented by the authors in 1954 made an immense impact, stimulating
theoretical work by Limber, Neyman and Scott
(Sect. 2.3.1). The first
Lick survey map is shown in Fig. 5. Also
important because of its far
reaching influence was the Princeton presentation of the Lick
catalogue and its analysis made 10 years later
(Seldner et
al. 1977).
It is shown for the northern and southern hemispheres in
Fig. 6.
1 Explanations in quotes are given in
square brackets; the quotes from Einstein, Heckmann, Weizsäcker,
Weyl and Wirtz are translations from the German originals.
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